Service

What is an intake manifold gasket and how does it work?

The intake on an engine may be made up of a lower intake manifold and an upper intake manifold or plenum. The lower intake manifold is a cast aluminum or molded plastic chamber bolted to the cylinder head of the engine. The intake manifold must be tightly sealed to the cylinder head(s) using a gasket in order to prevent air, oil, or engine coolant leaks.

When to consider replacing the intake manifold gasket:

Internal or external leaks. Due to constant temperature expansion and contraction of engine parts or overheating, the gasket’s ability to seal properly can be ruined, resulting in problems such as:

Internal or external engine coolant leaks. In some applications, the manifold has cooling passages within. If the manifold seal to the engine fails, coolant can leak externally or even into the engine oil crankcase, where coolant can be noticed in the engine oil.

Engine overheating. If the leak at the manifold is a leak of engine coolant, it can lead to engine overheating. However, there are other causes of engine overheating, so a mechanic would have to determine the actual cause.

External oil leaks. On some 6 and 8 cylinder engines, the intake manifold sits atop an oil-lubricated area of the engine block. If the manifold gasket has failed, oil can leak from the block to the exterior of the engine.

Poor engine operation, lean operation, rough idle. Vacuum air leaks into the manifold due to a defective gasket that will upset the air-fuel ratio. The engine may run poorly.

Check engine light. Minor leaks at the intake manifold gasket will not usually cause the check engine light to illuminate. However, as a leak persists, it may grow larger and it possible for the leak to degrade engine performance enough that it will cause a trouble code to set, which will cause the check engine light to illuminate.

How do mechanics replace the intake manifold gasket?

Working on a cold engine, the engine cover is removed.
If the intake manifold has internal cooling system passageways, the engine coolant is drained below the level of those passageways.

The accelerator cable assembly and cruise control cable are removed and set aside. All electrical connections and emission and vacuum lines in the way of the intake are removed. Ignition components, such as the coil, are removed as needed. If the car has an upper plenum, that is removed and set aside.

If the fuel rail is bolted to the intake manifold, the supply and return connections to the fuel rail are disconnected.

Once all connections to the manifold are clear, the manifold is unbolted and removed from the engine.

Aluminum and plastic manifolds are checked with a machinist’s straightedge to ensure the surface flatness does not exceed the original equipment manufacturer’s specification. If the surface of a manifold is not flat, the new gasket will not seal properly. Plastic manifolds are checked for cracks, heat damage, and warpage.

Once the manifold is deemed re-usable or replaced as needed, the new gasket is applied, the manifold is put in position and the mounting bolts are torqued with a calibrated torque wrench in the OEM specified sequence. In some applications, RTV sealant must be applied in corners of the mounting surface or specified hard-to-seal spots, per the service manual.

All removed components are then re-installed in the reverse of the above steps.

Finally, the vehicle is run and checked for leaks, and test driven.

Is it safe to drive with an intake manifold gasket problem?

Yes. The principal concern with a leaking intake manifold gasket is potential damage to the engine, depending on where the leak is. Although the vehicle will generally be safe to drive, you should schedule service as soon as possible to minimize the chances of additional costly damage. If the leak involves coolant, it could lead to engine overheating damage or the coolant could contaminate the engine oil, which can damage the engine bearings. If there is an air leak to the cylinders, it can cause lean operation which could overheat the catalytic converter.

When replacing the intake manifold gasket keep in mind:

In engines where coolant flows through the intake manifold, a leaking intake manifold gasket can be either the cause of or result of engine overheating. If you have a leaking intake manifold gasket, and the engine has overheated, the entire engine should be inspected for damage, such as a blown head gasket. The engine cooling system thermostat should be replaced because engine overheating can damage the cooling system thermostat.

Some car engine designs are more likely than others to experience leaking intake manifold gaskets due to material and design issues. Your mechanic can inform you if your car represents one of these cases. Many times a re-designed gasket, or altered installation technique and torque values, will be relevant to avoid a recurrence of any leaks. Mechanics will consult Technical Service Bulletins to determine if any unique circumstance exists for your car.